Studies in the Epidemiology Branch have identified associations between passive exposure to cigarette smoke during childhood and adulthood and risk for cancer at several sites in adulthood. Current studies were intended to provide additional evidence in support of some of these early findings. A prospective study of over 48,000 adults has recently been completed. In this study, the mortality and cancer experience of nonsmokers who lived with smokers in 1963 was compared with that of nonsmokers who lived with smokers in 1963 was compared with that of nonsmokers who did not live with smokers and with smokers. Study subjects were residents of western Maryland who had participated in a special county-wide census in 1963. At that time, demographic data and housing characteristics were obtained for 98% of the households in the county, and smoking histories were obtained for all residents who were at least age 16 in 1963. These data were used to derive a measure of exposure to smoke at home for each participant in the study. The cohort was followed through 1975 using existing records. Underlying and contributing causes of death were obtained for census participants who died in the county between 1963 and 1975. Cancer incidence was ascertained through a county-wide cancer register. Preliminary findings suggest that nonsmokers who live with smokers are at increased risk for death from all causes, at increased risk for death from arteriosclerotic heart disease, and at increased risk for developing certain cancers when compared with nonsmokers who are not exposed to smoke at home. Other early findings include a dose- response relationship for heart disease mortality and degree of exposure to cigarette smoke with the relative risk for heart disease death among nonsmokers living with smokers similar to that of active smokers of fewer than 10 cigarettes a day, and an inverse relationship between colorectal cancer risk and degree of smoke exposure. Other work in this area includes continued exploitation of the data collected in the study of childhood smoke exposure and adult cancer risk, and an additional study of sister chromatid exchanges and urinary mutagens in active and passive smokers which demonstrated small differences related to cigarette smoke exposure.